In Part One, three experiments investigated the effects of the surface structure of semantic illusion sentences upon semantic illusion rate (Chapters 3 to 6), but only a comparison of question and statements revealed any significant effects, with questions leading to more semantic illusion responses. To explore the implications of this lack of effect, a rating scale study was designed to provide an overview of how semantic illusion sentences compare to sentences used in ordinary discourse: semantic illusion type sentences were found to differ significantly from other sentences along a number of salient dimensions. In Part Two, three further experiments related semantic illusions to problem solving and examined the processing requirements of semantic illusions. Findings indicated that semantic illusions are subject to a kind of ‘functional fixedness’, which prevents thorough processing (Chapters 9 and 10). This may in part be explained by the load that semantic illusion sentences place on working memory, as was indicated by the results of two further experiments, which investigated the role that the different components of working memory play in semantic illusion processing (Chapter 11).